Both induced hypotension and hemodilution are being used as anesthetic adjuncts to reduce blood loss during major surgery and both may reduce cerebral oxygenation. The aim of this investigation is to determine the adequacy of measurement of brain electrial activity during hypoxia as an on-line clinical monitor of cerebral oxygenation during anesthesia and surgery. Changes in the electroencephalogram and cortical evoked potentials during hypoxia will be correlated with subsequent neurological, behavioral, and histological alterations in dogs. Studies will be performed with induced hypotension, alone and combined with hemodilution. Our goal is to determine the significance of varying degrees of change in electrical activity in regard to effects of neuronal function. These studies should help clarify the correlation between recorded electrical activity, and neuron viability, as well as determine the adequacy of brain electrical activity as reliable monitor of hypoxia.